Received this beauty in the mail today. I've played it for about 5 hours now. I'm in love with the low A sound, it's really warm and full, yet very detailed and you can hear the variations in your airflow very well, giving it lots of expression. It's tunable, but it arrived in tune: 14/16 whole tones were in tune before warm-up, 16/16 after warm up (did not check semitones). Warm up time is quite long, as you'd expect from a whistle with this much mass.
AIR: You'll have to blow rather hard if you're used to playing pennywhistles, and you'll have to play rather soft if you're used to playing 'true' low whistles. This flageolet is a medium whistle. it is relatively easy to overblow but the sustain takes quite some lung capacity.
FINGERING: The holes are aligned, not offset. This instrument can be played with the finger pads as you would a regular tin whistle, but you can also use a piper's grip. It's actually quite hard to use a piper's grip a the holes are relatively close together, but for players with smaller hands this might not be an issue. The edges of the holes are smooth and the holes are broad enough to have a 'sunken' feel to them, making them easy to locate.
SOUND: I chose the key of A because of the emotional color and I am not disappointed. This flute has a very mellow and warm, dark sound. There's this beautiful metallic resonance in the lower registers giving the flute a 'raspy' bottom. On the other hand, when applying the correct amount of air in the second octave, the highs are very smooth, not sharp at all. At the end of the second octave and the rest of the third the flute does get very loud, but it remains its warmth and silky upper end.
If you didn't get it by now, I'm absolutely in love with this thing. In the future I'll be buying more "The Busker" in different keys. I'm about to mail Thomann asking if they've got any hardcases I can use to store this baby in.
If you've got a few euro's lying around: you could buy 24 pennywhistles, or you can go all in and join the big boys with this beautiful Kerry Whistle.